Persist user rotations of external displays.

It also introduces a command line tool to rotate external displays for
testing purposes.

Instead of changing signatures of freezeRotation(), thawRotation() and
isRotationFrozen(), introduce 3 new methods to IWindowManager interface.
The old methods are being used pervasively.

Also resolved some style issues in DisplaySettings class.

Bug: 113252523
Bug: 111361251
Test: Rotation locks via settings still work. User rotation mode and
user rotation values for external devices are persisted as expected in
storage. DisplaySettingsTests passes.

Change-Id: I1746bea98a588f0bbd30c9f0617a7a23dc6e4209